This invention relates generally to high voltage transistor applications and more particularly concerns a circuit in which an optoisolator transistor is controlled by an input light emitting diode to turn on a series of high voltage MOSFETs for use in applications currently using a light emitting diode (LED) controlled with a high voltage light dependent resistor (LDR).
FIG. 1 shows an existing light emitting diode controlled with a light dependent resistor. A light emitting diode or LED 10 is positioned to shine light rays 12 onto a light dependent resistor or LDR 14. The LDR 14 is mounted on a substrate 16. When the LED 10 shines light rays 12 on the LDR 14, resistance of the LDR 14 changes. The resistance of the LDR 14 is linearly dependent on the intensity of the light rays 12.
Unfortunately, the response time of the LDR 14 is long and the device is sensitive to temperature change. A new circuit utilizing an optoisolator transistor controlled by an input light emitting diode to turn on a series of high voltage MOSFETs has been designed to replace the existing LDR. This new circuit has faster response times and is less sensitive to temperature changes.
Accordingly, it is the primary aim of the invention to provide a replacement circuit for an LED/LDR device which has faster response times and is less sensitive to temperature changes.
Further advantages of the invention will become apparent as tile following description proceeds.